1. Field of Invention
This invention relates to a manufacturing method for silicon substrates, and more particularly to a method for manufacturing silicon substrates having gettering capability.
2. Description of Related Art
In the manufacture of silicon substrates, the formation of dislocations is difficult to avoid if the ion implantation or annealing processes are incomplete. However, if the gettering set-up for the silicon substrate is incomplete, heavy metallic elements such as copper and aluminum will be trapped in the dislocation sites creating leakage paths. Therefore, the junction leakage current is closely related to how completely the gettering function is carried out. A well-established damaged layer formed on the bottom side of the silicon substrate is quite effective in containing the mobile heavy metallic atoms in subsequent high temperature processes, and hence is important for counteracting junction leakages at the dislocation sites. In addition, a good gettering capability for the silicon substrate makes it possible to reduce the gettering of heavy metallic ions onto the PN junctions, and thereby extending the lifetime of the integrated circuits.
FIGS. 1A through 1E are cross-sectional views showing the progression of manufacturing steps in the production of a silicon substrate having a gettering capability according to a conventional method.
As shown in FIG. 1A, the silicon substrate 10 has two faces, a first face 11 and a second face 12. First, the second face 12 of the silicon substrate 10 is etched, using a chemical etching method, to form a damaged layer 13 so that the silicon substrate is provided with the gettering capability. A total thickness of about 75.about.95 .ANG. can be chemically etched from the silicon substrate 10, for example, by using a potassium hydroxide solvent formed by mixing potassium hydroxide with deionized water in a molar ratio of 1 to 6 for about 1.about.3 minutes.
In FIG. 1B, a passivation layer 14 composed of silicon dioxide is then deposited above the damaged layer 13 using a chemical vapor deposition (CVD) method.
As shown in FIG. 1C, in the subsequent step, the silicon substrate is flipped over so that the first face 11 is now facing up. Then, two mirror processing operations are performed. Mirror processing is actually a chemical-mechanical polishing operation aimed at getting the required flatness for the first face 11.
Next, in FIG. 1D, an epitaxial silicon layer 15 is formed over the first face 11 by putting into an oxidation pipe furnace set to a temperature of about 1140 C for the reaction.
Finally, in FIG. 1E, the passivation layer 14 is etched until the damaged layer 13 is exposed, and then followed by subsequent processes.
Because of the time consuming and complicated manufacturing processes involved in the conventional method for fabricating silicon substrates with gettering capability, production cost is increased. Moreover, when the second face 12 is etched to form the damaged layer 13, a rough and uneven first face surface 11 will be generated due to the lack of a protective passivation layer. Therefore, mirror processing operations are necessary to get the required flatness before any subsequent processes can be carried out, and this will add to the complexity of the manufacturing operation.